This invention relates to electromagnetic door locks, and more particularly, to methods and devices for controlling the electromagnet of the electromagnetic door lock.
Electromagnetic door locks for the securement of a door to a door frame are well known. Conventional electromagnetic door locks employ an electromagnet which selectively electromagnetically bonds with an armature. One of the electromagnet and the armature is mounted to the door and the other of the electromagnet and armature is mounted to the door frame. A lock controller controls the energization of the electromagnet, and therefore the bonding engagement of the armature to the electromagnet.
In one form of an electromagnetic lock, commonly referred to as a shear lock, the electromagnet is mounted within a mortise in the door frame and oriented toward the edge of the door. The armature is positioned within a mortise in the door edge, whereby when the door is closed, the electromagnet and armature are in opposing relationship. These types of shear locks are particularly suitable for mounting on many types of swinging or double-acting doors. Also, shear locks are preferred for aesthetic reasons over door face mounted electromagnetic locks due to the concealment of the, electromagnet and armature.
Prior shear locks have attempted to compensate for the potentially inadequate securing force by providing for a mechanical engagement of the electromagnet and armature. The mechanical engagement is formed when the armature is electromagnetically bonded to the electromagnet. Conventional mechanical engagement configurations have included interlocking projections and recesses, such as disclosed in Frolov U.S. Pat. Re. No. 35,146. The mechanical engagement of the electromagnetically bonded armature and electromagnet provides a reliable and high level of shear resistance while still providing the advantages of the electromagnetic shear lock.
The armature and electromagnet are typically installed to form a gap between the components. The gap is required to allow for clearance so that the armature can swing past the face of the electromagnet as the door swings open and closed. Additionally, the gap can increase due to door sag and component misalignment. The armature is conventionally constructed to move toward the electromagnet to close this gap when the armature and electromagnet engage. The armature movement is also employed to facilitate the mechanical engagement of the projections and recesses. However, the electromagnet must generate a substantial electromagnet force to overcome the gap between the armature and the electromagnet and thereby engage the components.
The electromagnetic force of an electromagnet is proportional to the coil current. However, when the coil current is high, the electromagnet can generate significant heat. This may be especially critical when the electromagnet is mortised into a wood door frame. The wood door frame can thermally insulate the electromagnet therefore limiting the ability of the electromagnet to dissipate heat. Excessive coil heat can lead to failure of the electromagnet and a shortened lifetime.
A further limitation of many conventional electromagnetic locks, both shear locks and other arrangements, is that the locks are typically designed to operate at only a single voltage. Therefore, in many cases, manufacturers must produce, and distribute multiple models of electromagnetic locks which primarily differ only in the required input voltage. As a partial solution, some forms of field voltage selectibility for a given lock have been developed. The selection of the operating voltage can typically be implemented by the use of multiple wire leads, jumpers or by actuation of a switch. However, for each of the latter selection configurations, the electromagnetic lock is only capable of functioning at the preset voltage, whether that voltage is selected by the manufacturer or in the field at the time of installation.
Briefly stated, a lock controller in accordance with the invention selectively varies the current supplied to the coil of the electromagnet. The lock controller is preferably employed with an electromagnetic shear lock. However, the lock controller in accordance with the invention is also suitable for employment with electromagnetic locks mounted to the face of the door, and other arrangements of electromagnetic lock applications and designs.
During operation, a typical electromagnetic shear lock requires a high initial current to the electromagnet to produce a high level of electromagnetic attraction between the electromagnet and the armature. When the armature and the electromagnet are widely separated, this relatively large amount of magnetic force is required to attract the armature across the gap. Once the armature is in surface to surface contact with the electromagnet, only a smaller amount of electromagnetic force is required to be generated by the electromagnet. This electromagnetic force need only be sufficient to maintain the armature in place. The principal locking action between the electromagnet and the armature is accomplished by positive mechanical engagement of the electromagnet and the armature.
The lock controller in accordance with the invention preferably provides a high initial current to the electromagnet to close the gap between the electromagnet and the armature. The high electromagnetic force results from the high initial current supplied through the coil of the electromagnet.
After a preestablished time interval the lock controller reduces the current through the coil to an intermediate level. After the components are engaged, the reduced current is sufficient to maintain the electromagnet and armature in an electromagnetic bonding arrangement whereby the mechanical engagement is provided between the electromagnet and the armature. However, the reduced current through the coil lower power dissipation which results in favorable heating characteristics of the electromagnet that are not detrimental to the longevity or effectiveness of the lock system.
In the preferred form of the lock controller, the lock controller has a microcontroller and a switch assembly. The switch assembly selectively connects the electrical current to the coil of the electromagnet. The microcontroller actuates the switch assembly to turn on and off the current supplied to the coil to generate a pulse train having a modulated pulse width. The microcontroller, by use of the switch assembly, preferably generates periodic pulses of electrical current at a constant frequency. The average current is therefore controlled by varying the width of the pulse, or the amount of time the switch assembly is turned on. At the initial current level, the coil will have current directed through it for periodic predetermined amounts of time, or what is described as having a pulse of a certain width. At the reduced or intermediate current, the width of the pulse, or the period of time the switch assembly is on, is reduced. Therefore, the average current through the coil at the intermediate pulse width, is less than the average current through the coil at the initial pulse width.
In an alternate embodiment of the invention, the lock controller monitors the input power voltage supplied to the electromagnetic lock. The microcontroller controls or modulates the pulse width of current to the coil of the electromagnet in relation to the input voltage. Therefore, the lock controller automatically adjusts the coil current to compensate for the voltage supplied to the electromagnetic lock. Furthermore, even if the input voltage varies over time, the lock controller will continue to monitor and modulate the current to the coil to generate a suitable electromagnetic bonding strength regardless of the input voltage supplied to the electromagnetic lock. In one lock controller constructed in accordance with the invention, the lock controller can control the electromagnet for an input voltage range of from 10 to 35 volts.
An object of the invention is to provide a control system that controls the current supplied to the coil of an electromagnet.
Another object of the invention is to provide a control system for an electromagnet lock that controls the current supplied to the magnet coil in accordance with the operational status of the lock.
A further object of the invention is to provide a lock controller that can automatically adjust for changes in the input voltage supplied to the electromagnetic lock.
A still further object of the invention is to provide an electromagnetic lock that is efficient and reliable and exhibits favorable heat characteristics.